The present invention relates to indicator devices and, more particularly, to cyclometer register devices of a type employing a plurality of cyclometer wheels concertedly driven to provide an indication of a quantity.
Cyclometer registers are commonly employed in, for example, watthour meters for indicating an amount of energy consumption. Conventionally, a lowest-order cyclometer drum, having numerals 0-9 on its edge, is driven by gearing from a meter disk which, in turn, is driven at a speed proportional to the instantaneous power usage. As the lowest-order drum passes through a transition from 9 to 0, it drives the next-higher order drum to advance through an angle corresponding to one digit on its edge. As this drum, in turn, passes through the transition from 9 to 0, it drives the next superior drum through an angle corresponding to a single digit on its edge.
A common problem with cyclometer registers arises from the numeric ambiguity during the time that a numeric transition is occurring in one or more of drums, and a 0-9 transition in one of the superior drums. In a slowly moving register, common in watthour meters, a superior drum may require a substantial time to achieve its transition as it is driven by the smoothly turning lowest-order drum. Cyclometer registers are used for the basic purpose of indicating discrete digits in response to an analog input. This is intended to avoid meter-reading errors common in dial-type registers. The slow transition of superior drums is contrary to the purpose of cyclometer registers since, during the transition, a meter reader may misread the indications of partly-rotated drums.
One solution to this problem disclosed, for example, in British Patents Nos. 985,778 and 1,036,601, employs an eccentric weight freely mounted on a common shaft with all of the drums and driven by the lowest-order drum. At a predetermined angular position of the lowest-order drum, usually at its 9-0 transition, the eccentric weight becomes overbalanced and rotates by gravity until it strikes an element connected to the next-higher-order drum. This rapidly flips the next-higher-order drum through it's next digit transition without the slownes inherent in an apparatus without a free eccentric weight. If the next-higher-order drum is also in a position requiring a 9-0 transition, then it, in turn drives its superior drum rapidly through a single-digit transition.
The driving torque for watthour meters is made purposely as low as possible to minimize the burden, or power, required to produce it. As a consequence, watthour meters are sensitive to elements in their registers requiring torque to overcome. Although torque requirements having a constant value such as, for example, frictional resistance, may be reasonably compensated by providing the meter with greater torque, when torque requirements vary from time to time to produce variations in meter speed, meter accuracy may be adversely affected. Raising the free eccentric weight from its lowest position to its overbalancing position increases the torque needed to drive a cyclometer register. Then, during the free fall of the free eccentric weight, and during an ensuing period before the task of raising it resumes, the required torque is lower. Such torque variations either require increasing the available torque from the watthour meter or, in an extreme case, may produce a periodic or an overall metering error. The lowest-order drum in the referenced British Patents include a counterweight substantially balancing the eccentric weight as it is raised from its equilibrium position. This counterweight must be elevated during the half cycle before contact is made with the eccentric weight, and thus contributes to unbalanced torque requirements.